Lasers are known, and find application in a wide variety of fields, such as consumer products, medical devices, metrology, and industrial equipment for fabrication, cutting, dicing, heating and annealing. In general, a laser is an optical source that emits a coherent light beam (also referred to herein as coherent light). The coherent light may be emitted as a relatively narrow beam and may be focused to very small spots.
Because they emit coherent light, lasers may be prone to speckle. Speckle is a random intensity pattern on reflection from a diffuse surface generally caused by mutual interference of multiple laser beams from a coherent source reflected from different reflection points. For example, a coherent light beam may be scattered at a rough surface (e.g., a piece of paper, a display screen or a metallic surface). Coherent light scattered by the rough surface can exhibit variation in optical paths between any of two different raised areas on the surface, to produce an interference (speckle) pattern if the optical path is relatively shorter than the coherence length of the laser source. The speckle pattern is typically observed as a random granular pattern.
Speckle patterns may severely degrade the image quality of components illuminated with a laser source, such as laser annealing, laser projection displays and laser microscopes. Accordingly, it may be desirable to reduce or eliminate speckle from a laser source.